Mexico became independent from Spain in 1821, the same year as Perú. Plenty of Mexicans had already settled in parts of northern Texas, but not enough to work the land properly, so Mexico offered cheap land grants to Americans, and by 1830 at least 20,000 Americans, mostly southerners, had taken advantage of the offer.
The Government of Mexico decided, in a state of nervousness, to forbid any more immigration by North American settlers. At the same time the government got itself into hot water by trying to ban slavery, as it was already illegal in Mexico. As a result, Texans declared their independence from everybody, and set up their own Republic of Texas.
The dictator of Mexico, one General Santa Ana made up his mind to crush such insolence, and as a start his troops overran the Americans’ fortress at the Alamo and killed everyone, man woman and child, inside it, including some distinguished American heroes. Now was the time for Sam Houston to rally the Texans (‘remember the Alamo!’) and they smashed the Mexican army at San Jacinto, catching Santa Ana at the same time. The thwarted general was forced to recognise the independence of what was called the ‘Lone Star Republic’.
Texas then asked for admittance into the United States, but those in the North refused, as Texas would, if allowed, be joining the US as a ‘slave state’. On account of this, Texas had to wait (not patiently) until 1845 before, much helped by the current Secretary of State and the President, it was admitted as the biggest state in the Union.
The New York-based journalist and editor John L. O’Sullivan wrote a blazing article in 1885 justifying US control of the whole North American continent, including Mexico and Canada. The article raised a storm, but O’Sullivan claimed that no nation on earth should be allowed to interfere with America’s ‘manifest destiny to overspread the continent allotted by Providence (God) for the free development of our yearly multiplying millions’. There it was, in black and white, though the article was actually written to justify the annexing of the state of Texas. As we know, Texas became an American State in 1845 but it seems that the idea behind it was also to justify the occupation of another state – Oregon, and a large chunk of Mexico, seized after the Mexican-American War of 1846 – 48.
This kind of bruising talk was originally a Democratic slogan, but it was assumed by the Republicans as well when Alaska was bought, and the US fought the Spanish-American War. The phrase ‘Manifest Destiny’ can mean a lot of things, of course, but in O’Sullivan’s case it meant greed disguised as idealism, and the overwhelming wish of most Americans to join ‘the empire club’ – after all, many European countries had had their empires, or were in the process (Great Britain) of building one.